Immunodiagnosis, biosensor and the like for detecting a certain substance from among biomolecules such as protein or lipid have widely been applied as a means for the early detection or diagnosis of diseases. However, the non-specific adsorption of co-existent biomolecules onto the surface of biosensor which occurs simultaneously with a specific reaction interferes as background noise to prevent the achievement of high sensitivity. In the case of diagnostic particles, furthermore, not only the problem of background caused by non-specific adsorption but also dispersion stabilization in biological fluid or diluted liquid thereof has been a great issue. Inventors of this invention previously found that substrate which has, on its surface, a brush-like structure of water-soluble polymer such as polyethylene glycol not only retrains non-specific adsorption onto sensor surface but also improves dispersion stabilization of nanoparticles, and, thus, have provided materials as a new tool of biodiagnosis. As concrete examples of such inventions, a surface with brush-like structure of poly(ethylene oxide) having an increased density (e.g., WO 03/076933 A1), biosensor surface which carries a poly(ethylene glycol) segment-containing polymer derivative (e.g., Japanese Patent KOKAI Publication No. 2003-149245) and dispersion-stabilized functional metal fine particles and semi-conductor fine particles (e.g., Japanese Patent KOKAI Publication No. 2002-080903) can be mentioned.
In the above-mentioned inventions, biomolecules such as antibody are bonded to the tip of brush structure to serve as a system to sense, with high sensitivity, specific reaction such as antigen recognition. However, brush surface is very liable to prevent the adsorption of protein or the like, and, also for some other reasons, it is sometimes difficult to increase the amount of protein such as antibody supported on the tip of brush, which has been a bar to the achievement of high sensitivity. In another method, after antibody or antigen has been bonded to the surface of a solid phase, a polymer which is originated in glycosylethyl (meth)acrylate is adhered to redundant protein-binding sites on the solid phase surface, with a view to preventing the non-specific adsorption of impurity protein or the like which may be contained in sample for assay (Japanese Patent KOKAI Publication No. Hei 10-123135). There has also been proposed another method wherein the surface of a solid phase which is used for immune reaction is protected with a polymer originated in (meth)acrylate which has polyethylene glycol chain in place of the above-mentioned glycosylethyl (Japanese Patent KOKAI Publication No. Hei 11-287802).
These polymers, however, may be sometimes insufficient in bondability or immobilizability onto solid phase surface to which the non-specific adsorption of protein or the like needs to be restrained. Otherwise, when immobilizability is enhanced, it may adversely affect the specific bondability of antibody to antigen in immune reaction. In another proposed method, the affinity of a bio-specific bonding pair, e.g., the affinity between streptoavidin and biotin, is utilized. In detail, a biotinated antibody is bonded to a solid phase which has previously supported streptoavidin, and said solid phase is thereby coated with biotinated polyethylene glycol (Japanese Patent KOKAI Publication No. Hei 11-211727). When this method is to be employed, however, one of companion pieces to bio-specific bonding pair needs to be previously immobilized on solid phase surface.